1. Field of the Invention
The invention relates to a method of simultaneously balancing mechanically coupled, synchronously rotating rotors that have different axes of rotation and, in particular, balancing cylinders and/or rollers of a papermaking machine.
2. Description of the Related Art
To date, cylinder groups, in which synchronously rotating cylinders are driven by only one drive via a transfer case, are balanced by removing parts of the transfer case and then driving and balancing every cylinder individually via an accessory drive.
Such a procedure is, however, very time-consuming and sometimes linked with mechanical risks, as it is necessary to separate connections that have otherwise run during, possibly, years of operation.
Theoretical and practical tests have already been carried out in a considerably simplified laboratory test in which two synchronously rotating cylinders were balanced in a coupled state (Thesis by H. Wilhelm, Fortschritt-Berichte VDI, Reihe 11, xe2x80x9cBetriebswuchten gekoppelter Rotorenxe2x80x9d (Progress Reports VDI, Series 11, xe2x80x9cOperating balancing of coupled rotorsxe2x80x9d); H. Wilhelm, H. P. Wxc3x6lfel, xe2x80x9cBetriebswuchten von Walzen in Papiermaschinenxe2x80x9d (xe2x80x9cOperating balancing of rollers in paper-making machinesxe2x80x9d); Das Papier June 1997, Pages 297 to 302). These tests were carried out under considerably restricted conditions.
The present invention relates to an improved method of balancing rotors by which it is possible to balance coupled rotors that do not have a common axis of rotation (such as, e.g., turbo sets) in a state ready for operation and/or under near-practice conditions. The method facilitates balancing in the shortest possible time, i.e., with increased economic efficiency and without any mechanical risk. The method should, in particular, be applicable for dryer cylinders, guiding rollers, calender rollers and/or the like.
The invention comprises, in one form thereof, a method of simultaneously balancing mechanically coupled, synchronously rotating rotors that have different axes of rotation, in particular cylinders and/or rollers of a paper-making machine. In this method, the rotor group to be balanced is equipped with, respectively, at least one vibration pickup in every bearing plane and/or in at least one other measuring plane that significantly describes the vibrations of the rotor. As such, as many impulse and phase transmitters are installed in the rotor group to be balanced as are provided different angular velocities of the rotors. At least the pertaining vibration signals and the pertaining speed signal are simultaneously recorded with regard to a respective measuring plane. Applying the method of the coefficients of influence and setting defined test unbalanced masses, the coefficients of influence of every test balance plane are determined for every measuring plane, and at least one corresponding matrix of coefficients of influence is generated. The counterbalance mass distribution is determined for every balance plane of the rotor group from the generated matrix of coefficients of influence, the position of at least one test balance plane being preferably selected different from the at least one operating balance plane corresponding thereto.
The embodiment provides, inter alias, the following advantages:
1) Balancing a rotor group in a coupled state using easily accessible test balance planes is significantly faster than balancing the individual rotors successively or balancing thereof in a coupled state in which the test balance planes and the operating balance planes are identical.
2) Mechanical risks that are generated by decoupling rotors are completely prevented. Possible mechanical risks include, for instance, destruction of or damage to the gearwheels during disassembly, leakage of the gearbox after reassembly, torn off bolted connections and/or the like. Such mechanical risks are prevented by the method according to the invention.
In the above-mentioned thesis by H. Wilhelm, Fortschritt-Berichte VDI, Series 11, xe2x80x9cBetriebswuchten gekoppelter Rotorenxe2x80x9d, a balancing method using coefficients of influence for coupled rotors was already tested on a laboratory test rig. However, this was carried out under the restrictions that the positions of the operating balance planes and the test balance planes that were required during the test balancing runs were identical, and that, for the group of cylinders to be balanced, all the rotors present in the group were operated at a synchronous speed. The thesis did also not consider a combination of elastic and/or rigid rotors in a rotor group to be balanced.
Another difference to be emphasized is that, in connection with the method according to the invention, it is not necessary to measure at the bearings and that it is not necessary to measure the vibrations at all measuring planes, respectively, in the same direction. These are important aspects for practical use, as unobstructed access is not always possible at all bearing planes (cf., e.g., Nipco rollers in calenders), and as it is also not always ensured that the vibrations can be measured at all the relevant measuring planes, respectively, in the same direction.
Furthermore, the position of the operating balance planes (i.e., planes in which the counterbalance masses will subsequently be installed for continuous operation) need not be identical with the position of the test balance planes (i.e., planes in which test balance weights are installed only during the balancing process). To determine the matrix of coefficients of influence, it is rather advantageous to select planes for the test balance weights that are easily accessible and where test balance weights can be mounted and dismounted in the shortest possible time. The counterbalance weights that are determined by use of the matrix of coefficients of influence can be converted to the operating balance planes by the respective mathematical relations.
Rotor vibrations can be recorded by vibration pickups in one or more directions to be specified.
Triggers and/or the like can be used as impulse and phase transmitters.
The rotors can be dryer cylinders, guiding rollers, calender rollers and/or the like.
It is, for instance, possible to select at least one test balance plane in the area of a thread of a pulling screw that is associated to a cylinder cover. As has already been mentioned, the operating balance planes need no longer be identical with the test balance planes.
Balancing can be realized at a rotor speed that can be specified at will. In particular, for elastic rotors, operational balancing is advantageously carried out in the main operating speed range.
Should the rotor group to be balanced not exclusively be composed of rigid rotors but also or only of elastic rotors, the number of balancing planes per rotor must be increased according to the inherent shapes to be balanced. Various matrices of coefficients of influence are then preferably simultaneously determined at different angular velocities to be specified. If necessary, a counterbalance mass distribution, at which vibrations in the measuring planes are minimized for the selected angular velocity ranges, is then calculated by numerical averaging.
As almost all rotor groups to be balanced also include rotors, the angular velocity of which is different from the angular velocity of the rotors to be balanced and in which the naturally existing residual unbalances are not in a fixed phase position to the rotors to be balanced, suitable vibration signal processing is required to eliminate the respective interfering influences. For this purpose, vibration signal processing is preferably carried out, in which the complex rotary-frequent vibration parts are determined from the recorded time signals by Fourier transforms, this step being repeated various times, the determined complex vibration parts being subsequently averaged, and the matrix of coefficients of influence being determined from the averaged complex vibration parts.